1. Field of the Invention
The present invention relates to an image reading apparatus, and particularly to an image reading apparatus in which an object placed on a mounting unit is imaged or photographed by an imaging unit.
2. Description of the Related Art
Image information of an object is obtained by imaging or photographing the object by an imaging unit such as a camera in a conventional image reading apparatus. However, when the object includes a shiny portion or material that is easily subjected to specular reflection of light, the specularly reflected light may be directed to a camera. In this case, the camera may capture or image the specularly reflected light. It is sometimes difficult to obtain clear image information of the object because the specularly reflected light appears overexposed. Therefore, specularly reflected light is prevented from being directed to a camera in some conventional image reading apparatuses.
Japanese Patent No. 2921922 discloses, for example, a tablet testing device in which a first polarizing filter is arranged between a lighting device as a lighting unit and a tablet as an object, and a second polarizing filter is arranged between a camera as an imaging unit and the tablet. Thus, light polarized to have a predetermined polarizing angle by the first polarizing filter can be emitted to the tablet and light specularly reflected by a wrapping material of the tablet is shielded by the second polarizing filter. Therefore, it is possible to prevent specularly reflected light from being imaged by the camera. Consequently, clear image information can be obtained.
However, when an object is easily subjected to specular reflection of light, light from a light source of a lighting device may be specularly reflected on the object. In addition, an imaging unit that images the subject or a supporting member associated with the imaging unit may be reflected on the object and imaged by the imaging unit. In other words, when the object is imaged by the imaging unit, the imaging unit or the supporting member may be taken in with the object. Thus, when the imaging unit may be taken in an image taken by the imaging unit, the image taken by the imaging unit easily becomes unclear. Therefore, it is very difficult to obtain clear image information irrespective of an object material.